KSZ8794 question

I am in the process of spinning up a board with a KSZ8794 chip on it. It’s basically a 4 port ethernet switch where one port is the RMII interface and the other three are normal ethernet connections. This is useful to integrate a small switch on my PCB :slight_smile:

This chip allows for communication over both MDIO and SPI. The choice is for the end user.

Since I would like to send a board over to GHI (so they can make it work in TinyCLR :slight_smile:), I would like to know if I am best off connecting the MDC and MDIO pins or should I hook it up to a available SPI on the SC20100S?

I am not sure how SPI would work here! If this chip is ethernet PHY then SPI would/shouldn’t work!

I haven’t looked at datasheet BTW

It has three built in PHYs. I’m also not entirely sure.

I know that the SPI and the MDIO pins on the chip are the same pins, so I can’t just connect both.
I think a reason to use SPI would be to get access to the VLAN management of the IC, since it is a managed switch ic.

This may be a somewhat simplistic answer, but based off of my 3 minutes of google-fu MDIO is designed specifically for ethernet chips - is there any reason to not use it? looking at the data sheet, SPI runs at a higher clock, but that seems to be the only difference.

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Then my guess is that you are required to have both. SPI is configuration and RMII for data.

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And if that is the case then the driver will not be simple is my guess

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Gus, I think you might be confusing RMII and MDIO.

MDIO and MDCLK are the data lines for configuration etc for RMII, as far as I understand. This chip allows to use either these two pins or SPI. Switching at runtime isn’t possible because the SPI and MDIO MDCLK pins aren’t the same on SC20100 but are on the PHY

oh I see. We have only used MDIO/MDCLK in the past, didn’t even know there is an SPI option!

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